The human malaria parasite, P. falciparum, utilizes multiple ligand-receptor pathways, known as invasion pathways, for the invasion of human erythrocytes. This allows the malaria parasite to respond to polymorphisms in erythrocyte receptors and/or evade the immune system and may be a determinant of virulence. This research will be done primarily in Dakar, Senegal at the University of Cheikh Anta Diop in collaboration with Dr. Ousmane Sarr, Prof. Souleymane Mboup and Mr. Ambroise Ahouidi, as an extension of the Fogarty International Center grant (D43 TW0011503). Previously, we have identified the common usage of multiple invasion pathways in Senegalese isolates and the expression of multiple paralogs of the PfRh family. We will test the hypothesis that sequence and expression polymorphism in members of the PfRh family are driven by the humoral immune response. Importantly, this proposal focuses on uncultured field isolates from regions of different malaria endemicity within Senegal. To accomplish these goals our specific aims are as follows: 1) We will analyze in detail the extent of expression variation and sequence polymorphism of parasite invasion ligands of the PfRh family that have been implicated in erythrocyte invasion in isolates obtained directly from patients in Senegal. 2) We will measure humoral immune responses to specific domains of the PfRh proteins. We will assess the invasion inhibition potential of antibodies derived from exposed patient sera using PfRh-knockout parasite lines. An understanding of the relationship between the use of multiple invasion ligands and the development of protective immunity is a pre-requisite to their inclusion in the development of a vaccine. PUBLIC HEALTH RELEVANCE: In collaboration with the University of Cheikh Anta Diop, we propose to analyze in detail the extent of variation in levels of expression and sequence of the PfRh family of invasion ligands, an uncharacterized family of molecules that are postulated to play a role in both virulence of the parasite and immunity. The present proposal presents two novel aspects that have developed from previous work in Senegal. Firstly, we will consider in depth, the nature of expression and sequence polymorphisms of members of the PfRh family. Secondly, we will measure immune recognition of this important family that has not been previously studied at all. The data we obtain will have important implications for the inclusion of these molecules in the development of vaccines against malaria.